1. Field
This disclosure relates generally to invisible color-changing ingredients in various marking devices that result in multi-colored changes when applied over a specially treated printed or coated surface.
2. Background
Invisible inks have been utilized on documents for a wide range of purposes, from anti-counterfeiting measures to games and entertainment items. Invisible inks include “scratch inks” or inks that produce a color change or color initiation by rubbing, scratching, wiping, applying pressure or other heat producing actions. Examples of invisible inks are disclosed in U.S. Pat. Nos. Re. 36,306 and 8,053,494 B1, the entire disclosures of which are incorporated herein by reference. Invisible inks may include a leuco dye color former and an activator. The combination of the leuco dye and the activator produces a color change, when combined in the presence of heat generated by, for example, rubbing, scratching, wiping, applying pressure or other heat producing actions.